Key Engineering Materials Vols. 645-646

Abstract: A vibration sensor based on electrochemical principle can be widely used in the field of seismology. For its instinctive bandwidth is limited, compensation by circuit is essential to expand the bandwidth. This article presents a method of frequency compensation by circuit based on the original amplitude-frequency characteristic of the electrochemical vibration sensor. The bandwidth is broadened obviously from 2s-10Hz to 25s-20Hz. The noise performance of the final output compared to the CME6011 is also presented.

Abstract: A novel micro-machined out-of-plane resonant accelerometer with a differential structure is presented. The micro-machined accelerometer consists of two identical torsional structures with asymmetric mass distribution, torsion beam and two different-height resonant beams. Due to the asymmetric mass distribution, the two mirror-symmetrical-placed torsional structures turn an angle under an out-of-plane acceleration, which makes the different-height resonant beam connected to the structures bear different axial stresses, outputting a differential resonant frequency shift. A multi-layer mask etching process based on silicon-on-glass micro-machined technology was employed to fabricate the differential structure and the different-height resonant beams. Primary experiment shows the differential sensitivity of out-of-plane acceleration is 32Hz/g at the resonant frequency of 21.41 kHz.

Abstract: On the basis of analyzing the boot process of silicon micromechanical gyroscope on a chip at room temperature, -40 °C and 60 °C constant temperature environment, for the character that the gyroscope can realize the compensation function and possess temperature-sensitive output model, This paper analyzes the relationship between the bias and temperature meter, and presents compensation method of the initial bias so as to reduce different turn-on time caused by the variation with the temperature of working environment. Experimental results demonstrate the method can effectively reduce turn-on time at the variation with temperature of working environment.

Abstract: Nowadays, most of scholar study the 2D indoor positioning system based inertial sensors. But in some case, the information of 3D space about person is very important, such as mine accident, fire rescue, and so on. In this paper, we focus on designing and implementing a 3D indoor positioning system based on MEMS sensors and barometer sensor. The MEMS sensors including a three-axis accelerometer, a three-axis gyroscope, and a three-axis magnetometer is used for acquiring information of human movement. Barometer sensor is used to measure the height of the person where he is. Then the collected raw data is sent to a PC by a MCU wirelessly. Thus the performance of the 3D indoor positioning system is optimized by moving data post processing to a PC. In a 3D indoor positioning system, the integral drift and the heading drift are the main sources of the errors. Therefore, a method which is the combination of the zero velocity updates and the sensor data fusion based on an extended Kalman filter is proposed. Further improvement on the accuracy of positioning can be achieved by removing the static biases. A novel method including compensating the sensor biases based on experiment is presented. These methods have been carefully investigated through theoretical study and simulation. The simulation results indicate 3D indoor positioning is achievable through the application of the presented methods.

Abstract: In this paper, temperature characteristic of a previous developed nickel-chromium (Ni-Cr) thin film atmosphere pressure sensor is analyzed caused by residual gas. As expected, the output signal of the previous fabricated sensor increases with atmosphere pressures. But when pressure load is fixed, the voltage-temperature characteristic is nonlinear. One factor of this effect is residual gas. Based on the pressure-displacement equation of membrane, the gas balance equation and Provided that the deformation of membrane is spherical crown, the relationship equation of relative change of piezoresistor is defined. Studying the First order derivative and second order derivative of relationship equation of relative change of piezoresistor, it is proved that the residual gas will affect the temperature characteristic of previous designed sensor.

Abstract: Film bulk acoustic wave resonators (FBARs) with relatively high Q-factor are considered good candidates to be used in the RF module of chip-scale atomic clocks (CSACs). In order to simulate and analyze the resonant properties, the Mason equivalent circuit of the FBAR device is introduced, which consists of five parts including top electrode layer, low temperature silicon oxide layer, piezoelectric layer, bottom electrode layer and a composite support structure layer. With the practical processing conditions considered, the piezoelectric layer with a reasonable thickness of 1.30um is selected to achieve a FBAR device with resonant frequency 4.60GHz and Q-factor 278 by the simulation and analysis. In order to further improve the Q-factor, SiO₂ thin films with thicknesses from 0.10um to 0.50um placed between the top electrode and piezoelectric layer are introduced. However, as the SiO₂ thin film is introduced, the resonant frequency of the FBAR device will drop. In order to keep the resonant frequency fixed to 4.60GHz, the thickness of the piezoelectric layer is adjusted. Finally, the FBAR device resonating at 4.60GHz with Q-factor 627 is achieved, the thicknesses of the SiO₂ film and piezoelectric layer of which are 0.20um and 0.69um respectively. The Q-factor of the FBAR device improves about 350, and the FBAR device is expected to be used in CSACs.

Abstract: In this paper, a modeling and simulation method for planar interdigitated ruthenium oxide MEMS supercapacitor was proposed based on the electrochemical reaction mechanism of supercapacitor. The study simulated the planar interdigitated ruthenium oxide MEMS super capacitor using Comsol software. The highly accurate charge and discharge curves of the super capacitor, electric potential distribution graph and the concentration distribution graph were got through simulation. The effects of two structure-parameters were discussed in the research.

Abstract: In this paper we used the MEMS microphone to detect the sound position. A four–microphone array was constructed to localize sound source with Time Difference of Arrival (TDoA) measurements based on hyperbola model. The time delay was calculated using Generalized Cross Correlation (GCC) algorithm. A practical test system was built to confirm the feasibility of the hyperbola model and GCC algorithm using MEMS microphone. Data were collected in field experiments and calculated on PC by matlab. The results show that the method instructed in this paper is feasible in localizing the sound position with MEMS microphone.

Abstract: This paper presents the design, fabrication and tests of an electro-magnetic vibrating ring gyroscope based on a control system and SOI-MEMS technology. The control system, including variable gain control (VGC), drive-frequency control and regulation module, is designed to improve mode matching. In device fabrication, and buffered hydrofluoric acid (BHF) solution is used to remove the buried oxide layer and release the suspended spring. Meanwhile, a compensate disk and negative photo resist (AZ303) coated on the backside of the wafer are employed to weaken the Lag and Footing effects during through-wafer etching process. The design of the gyroscope is optimized by FEA simulation and the fabricated devices show a rather good performance.

Abstract: A universal capacitive readout integrated circuit MS3110 is used to measure capacitances in micro capacitance sensor. The configuration, operating principle and process of MS3110 are introduced and a method of programming the inner register on-chip with STM32 is presented with the control block diagram. Performance of MS3110 has been tested by the inner adjust capacitance. A comb micro accelerometer is designed and manufactured. A tentative equivalent electric model of accelerometer is built according to a series of capacitance tests, and the influence of parasitic capacitance in accelerometer system is discussed.